Add ability to render an IconButton as the SelectPanel anchor (primer#3731)

Co-authored-by: kendallgassner <15275462+kendallgassner@users.noreply.github.com>
Co-authored-by: Joyce Zhu <joycezhu@github.com>

Author: kendallgassner

.changeset/fruity-rooms-travel.md

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+---
+'@primer/view-components': patch
+---
+
+Updates SelectPanel anchor to allow IconButtons

.playwright/screenshots/snapshots.test.ts-snapshots/primer/alpha/select_panel/select_panel_with_icon_button/aria-snapshot--after-interaction.yml

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+- button "Menu" [expanded]
+- dialog "Menu":
+  - heading "Menu" [level=1]
+  - button "Close"
+  - text: Filter
+  - searchbox "Filter"
+  - listbox "Menu options":
+    - option "Item 1"
+    - option "Item 2"
+    - option "Item 3"
+  - text: 3 results tab for results

.playwright/screenshots/snapshots.test.ts-snapshots/primer/alpha/select_panel/select_panel_with_icon_button/aria-snapshot.yml

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+- button "Menu"